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| From | Isobel Williams <iwilliams24@hotmail.com> |
| To | "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu> |
| Subject | st: Losing Observations in Logit |
| Date | Sat, 1 Mar 2014 13:48:32 +0000 |
Dear All, I am running a logistic regression, and then pairing them using propensity score matching. Within the dataset, I have divided the data into groups A, B, and C: generate groupA=1 if zona==1 replace groupA=1 if cla_tam==1 replace groupA=1 if h_selec==1 replace groupA=0 if zona==0 replace groupA=0 if cla_tam==2 replace groupA=0 if cla_tam==3 replace groupA=0 if h_selec==0 replace groupA=0 if h_selec==9 generate groupB=1 if zona==1 replace groupB=1 if cla_tam==1 replace groupB=1 if h_selec==0 replace groupB=0 if zona==0 replace groupB=0 if cla_tam==2 replace groupB=0 if cla_tam==3 replace groupB=0 if h_selec==1 replace groupB=0 if h_selec==9 generate groupC=1 if zona==0 replace groupC=1 if cla_tam==1 replace groupC=1 if h_selec==0 replace groupC=0 if zona==1 replace groupC=0 if cla_tam==2 replace groupC=0 if cla_tam==3 replace groupC=0 if h_selec==1 replace groupC=0 if h_selec==9 when I run the tab command for all groups, Stata tells me that: . tab groupA groupA | Freq. Percent Cum. ------------+----------------------------------- 0 | 45,316 58.47 58.47 1 | 32,187 41.53 100.00 ------------+----------------------------------- Total | 77,503 100.00 . tab groupB groupB | Freq. Percent Cum. ------------+----------------------------------- 0 | 63,277 81.64 81.64 1 | 14,226 18.36 100.00 ------------+----------------------------------- Total | 77,503 100.00 . tab groupC groupC | Freq. Percent Cum. ------------+----------------------------------- 0 | 56,780 73.26 73.26 1 | 20,723 26.74 100.00 ------------+----------------------------------- Total | 77,503 100.00 However, when I run a logistic regression on propensity score matching between groups A and B, Stata tells me that I only have 7099 observations. Furthermore, when I wrote the code for keep if, the programme says "63227 observations deleted". Here is what I tried to do in estimating a logit propensity score and match (nearest neighbor) between groups A & B: preserve keep if groupA==1 & groupB==1 logit treat floor fmiss wall hhinc2.... predict double ps1 psmatch2 treat, outcome (S06A20) pscore (ps1) caliper(0.2) common logit restore The objective is to estimate a logit/propensity score and match observations from group A with group B. Any help on this matter would be very much appreciated. Many thanks, Isobel Williams * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/